Method of starting electric motors



Sept. 11, 1923.

w. ZEDERBOHM 1 METHOD OF STARTING ELECTRIC MOTORS Filed Aug. 23. 1919Patented Sept; 11,

UNITED STATES WILLY ZEDEBBOHH, OF BEBLIN-CHAB LOTTENBUBG,

SIEMENS- SHUCKERTWERKE GESELLSOHAI'T MIT BEBCHRANKTER -HAFTU' NG, OF.

PATENT OFFICE.

GERMANY, 'ASSIGNOB TO BERIJN, GERMANY, A. CORPORATION OF GERMANY.

hIETEOD OF STARTING ELECTRIC MOTORS.

Application filed August 28, 1919. Serial No. 819,516.

To all whom it may concern:

Be it known that 'I, WILLY- ZEDERBOHM, residingatBerlin-Charlottenburg,Germany, have invented certain new and useful Imrovements in Methods ofStarting Electric otors (for which I have filed application in GermanyMay 2, 1918, Ser. No. 48,240), of which the following is aspecification.

My invention relates to the startm of electric motors and moreespecially t ree phase motors, and its particular object is to arrangethe connections for starting the motors in such .a manner as to obviatethe drawbacks connected with the systems now in use.

It is. well known to start three phase motors, by connecting the statorwinding to thesystem at first in star connection and, after a certainnumber of revolutions has been attained, to change the windings fromstar over to delta connection. In doing this, however, the current mustbe' interrlzipted and the motor is currentless and fiel ess Onconnecting the fieldless motor to the full 5 voltage of the system thereresults a violent rush' of switchin -in current which ma cause theoverloa cut-outs to be release the fuses to blow and other troubles toarise.

This drawback is obviated according to.

so the present. invention by changing from star over to delta connectionwithout interruptingthe field, by way of intermediate connections, inwhich some current carrying contacts arec'onnected with the windings b:5 connections which belong to the star as we as to the delta type. c

The change of connections mentioned above can be efiected in differentways. In

the drawings aflixed to this specification and.

'forming part thereof three modifications of the connecting systemembodyin my invention are illustrated, Figs. 1, 8 an 9 showing thedifferent connection types, While Figs. 2 to 7 8' to 8 and 10 to 13merely illustrate I the succeeding phases of connection.

Referring to the drawings, Fig. 1 show the ends 0:, 3 2, of therespective phasesa b, c, which are next to the star point, and designedto be connected etc by step to the 0 leads 4), 'w, u, respectively, 0the phase nextfollowing in the cycle. Three throw-over switches d, saidswitches being connected to the ends av, y, z of the phases, whoseback-poles 9,,

e, f are provided to this end, b

12. 2', are connected to the star point, while the back-poles 9,, 1a,,2', are connected to the lead of the phase next-following in the cycle.If now these said switches are oper- .ated one after the other, thereresult the contact a: to g,. When switche is released at k,, theresulting distribution of pressure within the motor is illustrated by Fi5, winding (1 being connected in delta fas ion, while winding c isconnected to zero after star fashion. "By connecting e to h thereresults the distribution of pressure illus-.

trated in Fig. '6, where. the windings a, b belong to the deltaconnection. On changing switch 7 from i, to i, there results the deltaconnection shown in Fig. 7. Instead of switch 7 the end 2 may remainconnected with the star connection'and in the last step, where it ischan d over to delta, end 2 may be connectedwit origin u by aid of asimple switch.

The connections need not be made in the sequence described and they mayalso be varied in many directions. Thus for instance a throw-overswitch, instead of being connected to the end of a phase, may as we beconnected to the star point and the back poles of the said switch may beconnected with the lead and the end of-the base respectively, as shownin Fig. 8. In t is figure the turnln point e is connected to the staroint, the ack pole m, to the end 'of'phase and the back pole m, to thelead '0 of this phase. This figure also shows a single 1e switch isconnecting the end 3 of phase b with the lead u of the phase a. T e modeof starting the motor is similar to the one followed with thearrangement illustrated in Fig. 1. The connections need not be madesingly, one after the other, as it is quite feasile to maketwo or moreconnections at a time.' By suitably arranging the switches on acontroller the changing over may be effected quickly, there being nodanger that in certain cases such as the monophase connectionillustrated in Fig. 5 the motor might break down with a weak field andstop altogether.

Foo high currents in the single phases with nnsymmetric connections canbe obviated by inserting before the phase in question, such as phase a(Fig. 8) a resistance '71. provided with a short-circuiting device 0. Inview of this resistance being adjusted for a short interval only, it maybe made rather weak, such as the protective resistance in a protectiveconnection.

The eration of the arrangement according to iig. S is as follows: Atfirst the switch is is left open and switches d g, and e m, are closed,whereby the winding is arranged in star-connection as shown in Fig. 8Thereafter switch d g, is opened and thereby the Winding a separatedfrom the center. At this moment the motor runs with the two windings band a, current being supplied as shown in Fig. 8*. Then switch is isclosed so that the motor now runs in the socalled V-connection, in whichthe three potentials are connected with the two windings i5 and c as isshown in Fig. 8. Thereafter switch d gis closed whereby the end a ofphase a is connected with the beginning of phase 0. This connection isillustrated in Fig. 8, in which 0 is common to the stardelta connection.Hereafter switch em, is owned and the distribution of potential isobtained in the motor in accordance with the diagram shown in Fig. 8*.Lastly by closing switch e m the complete delta-connection as shown inFig. 8 is obtained. Thus also by this method at no time interruption ofthe field occurs.

A different mode of changing over from star to delta withoutinterrupting the field is illustrated by Figs, 9 to 13. Here the starconnection is formed of a plurality of star systems a 6 c and a,, b,, a,respectively, which are connected in parallel without their star pointsbeing connected, the said system being changed over from star to deltaone after the other as shown in Figs. 9. to 13. First the star point ofone system is opened (Fig. 10) and the said system is changed over todelta by itself (Fig. 11), this being once more a connection where themains are connected to the winding in such a manner that there resultconnections which belong to the delta as well as to the star type,system a 5 0 being connected in star and system a,, b 0 in deltaconnection.

Thereupon the star point of the second system is opened Fig. 12) andthis system is changed over to delta as well. There is no phase of thechanging-over procedure where the motor is currentless. The arrangementdescribed further offers the advantage, that the windings are always fedsymmetrically. It is true that the winding systems present relativephase differences of the elec tromotive force, resulting in acompensating current. However this compensating current will neverattain in the system a magnitude similar to that of the rush arising onthe fieldless motor being started. In order to keep the compensatingcurrent low in case that it should be too strong, resistances may beconnected here also in series with the single phases and theseresistances should also be chosen equal to the usual protectiveresistances.

In the last mentioned modification the changing over from star to deltais effected in two main steps, the star connected winding being dividedinto two systems. If it is desired to have more than two main steps, thestar-connected winding may be further divided.

I claim:

1. The method of starting a three phase motor by changing theconnections of its field winding from star to delta without interruptingthe motor field, which comprises successively disconnecting the end ofeach single phase winding from the star point and connecting it to oneof the three-phase leads.

2. In a device of the kind described in combination a three phase motor,the phase windings of said motor being connected in star fashion,throw-over switches connected to the ends of two of said windings and aswitch connected on one side to the end of the third )hase and on theother side to the lead of the phase next-succeeding in the cycle.

3. In a device of the kind described in combination, a three phasemotor, the phase windings of said motor being connected in star fashion,throw-over switches connected to the ends of the first and second ofsaid windings, while the back poles of the first switch are connected tothe lead and end of the second base, the back poles of the second switcheing connected to the lead and end of the third base and a connectionbetween the end of the third phase and the lead of the first phase.

In testimony whereof I afiix m si nature.

W ILLY ZEDEl iB HM.

